Yesterday I was alerted to a problem on one of my web pages. One of the photos I used (of storm damage) was instead a "girlie" pic! And just now, a different photo on a different page was instead showing some cocktail glasses. This appeared only on 3 different Verizon 3g and 4g phones. No other device showed the rogue photos. And the rogue photos disappeared later.

So it seems like the phone's browser is loading substitute images. How can that be?

I'd also advise you to double-check your site and make sure that there are no files there that shouldn't be. Likewise, check all the existing files to see if they've been modified (or delete everything and upload clean copies from your computer).